1. Field of the Invention
The present invention relates to an apparatus for measuring electrolytic corrosion and providing a qualitative indication of the amount of electrolytic corrosion. More specifically the present invention relates to an apparatus for providing an indication associated with an amount of electrolytic corrosion which occurs in an electric conductor installed in contact with the earth.
2. Description of the Prior Art
In almost all electric railways, the electric cars are energized by a DC voltage source. Typically, a DC voltage is supplied between a supply line and a rail in view of the fact that the rail is a good electric conductor. The electric car is thus supplied with the electric power from a supply line and a rail, while the car moves along the rail. The fact that the rail is installed in contact with the earth, however, can cause an undesirable situation. More specifically, as is often the case with a city or town, other electric conductors, such as water pipes, gas pipes, telephone cables, power cables and the like, are installed in the earth, which can extend along and in the vicinity of the rails of the electric railways. Therefore, it can often occur that a portion of the power current of the electric railways flows through the earth and the adjacent other electric conductors by way of leakage. It has been well known that electric conductors, such as rails, pipes, cables or the like, installed in contact with the earth are corroded in an electrolytic manner, as a result of leakage current flowing from the conductor to the earth. Thus it is most important that those who maintain such electric conductors are aware of the tendency of such corrosion occuring in the conductor.
A typical prior art method of providing an indication associated with an amount of the corrosion occuring in an electric conductor installed in contact with the earth and thus a qualitative measurement of the amount of corrosion is as follows. A change in voltage as measured between the electric conductor and an earthed reference electrode installed in ideal, good electric contact with the earth is recorded on a record medium, such as a record sheet. The area of the waveform thus obtained is calculated, the area of the waveform being representative qualitatively of the quantity of electricity carried by the leakage current, which in turn is closely related to the amount of the corrosion. However, such a method is disadvantageous in that it is very tiresome and of low accuracy. Another prior art approach to measure qualitiatively the amount of corrosion comprises utilization of a silver or copper coulometer, in which the amount of silver or copper, and specifically the weight thereof deposited within the coulometer due to flow of leakage current caused by the conductor-to-earthed reference electrode potential indicates the leakage current, and thus the amount of corrosion. This approach is also of low accuracy. It is desired to provide an apparatus capable of measuring qualitatively with ease qualitative indication of the amount of electrolytic corrosion which occurs in an electric conductor installed in contact with the earth.
A voltage storing device of interest in connection with the present invention is disclosed in U.S. Pat. No. 3,753,110, issued Aug. 14, 1973 to Hironosuke Ikeda et al. and assigned to Sanyo Electric Co., Ltd. the same assignee as that of the present invention. As set forth in the referenced patent, Professor Takehiko Takahashi and Assistant Professor Osamu Yamamoto, Technological Department of Nagoya University, announced their study on the electrochemical potential memory device by the use of a solid state electrolyte at the 22nd annual assembly of Japan Chemical Association held on Apr. 5 to 7, 1969. Briefly stated, this device comprises an Ag electrode as a cathode, an Ag-Te alloy electrode as an anode, and a solid state electrolyte having high ion conductivity, such as RbAg.sub.4 I.sub.5 sandwiched between both electrodes. When a DC voltage is applied to the device so that the Ag electrode may be negative, a portion of Ag contained in the Ag-Te alloy electrode migrates over to the Ag electrode, resulting in a decreased activity of Ag in the Ag-Te alloy, and thus an increased potential difference between both electrodes. The inventors of this device termed this state of operation as "charging". When the polarity of the applied DC voltage is reversed to that of the former case, Ag migrates back to And is refilled into the Ag-Te alloy resulting in the potential difference decreasing and returning to the initial value eventually. The inventors of this device termed this state of operation as "discharging". Study disclosed by the inventors of this device indicated that the electromotive force generated by the abovementioned charging or discharging current underwent linear change to some extent with respect to the charging or discharging quantity of electricity (current-time). Thus, this device makes it possible, as an outstanding characteristic, to do write-in and non-destructive read-out operations while preserving a relatively linear relation between the charging or discharging time and terminal voltage, and in addition, it can hold the memory condition for a relatively long period of time. These advantages mean that this device has potential use as an analog memory device. The referenced patent further discloses an improved electrochemical potential memory device. More specifically, FIG. 6 of the referenced patent shows both an improved electrochemical potential memory device for eliminating the IR drop across the resistance of the electrolyte and the overvoltage caused by dissoluion or deposition of Ag, which improved device is basically characterized by the provision of an auxiliary cathode that comprises an output terminal for detecting the potential separately from the abovementioned cathode utilized as the input terminal for the current conduction.
In view of these advantageous characteristics of the abovementioned memory device, the present inventors recognized that it is possible to utilize this device as an essential component of an apparatus for measuring electrolytic corrosion by measuring the quantity of electricity related to the leakage current flowing from an electric conductor installed in contact with the earth. The present invention has thus been accomplished by the inventors in order that such possibility may be realized.